The disclosure relates to a position controller for a pneumatic field device, such as a pneumatically driven control valve or safety valve, of a process plant, such as a refinery, a food product plant, a brewery, or a petro-chemical plant, or the like.
Position controllers used in process plants have to face high requirements regarding operational safety, control accuracy and ease of maintenance. When processing hazardous substances or products which have to be hygienically flawless or flawless in their composition, high costs arise from malfunctions of individual process control components and/or maintenance service as well as downtimes possibly related thereto.
A flexible pneumatic actuator system having a position controller for driving a control valve of a process plant is know from DE 10 2012 021 388 A1. The known actuator system solves complicated control engineering tasks in that the pneumatic actuator comprises several I/P-transducers for creating several control pressure signals and leads the control pressure signals together before they act upon the working chamber. Through the plurality of I/P-transducers utilized in the known actuator system, the risk of malfunction is increased. Statistical investigations have shown that errors of pneumatic actuator systems can often be traced back to defects of I/P-transducers and pneumatic amplifiers because these are subjected to electromechanical as well as fluid mechanical loads. In the known pneumatic actuator system it was shown that even a defect in just one I/P-transducer leads to an impairment of the entire actuator system. For applications with a high demand of availability or safety-critical plant parts the known system can thus only be used to a limited extent.